1. Field of the Invention
This invention relates to a rubber composition which gives vulcanizates having improved ozone cracking resistance and oil resistance. More specifically, the invention pertains to a rubber composition which comprises a partially hydrogenated acrylonitrile-conjugated diene copolymer rubber and a sulfur vulcanizer system, and which gives vulcanizates having improved weatherability, ozone resistance and sour gasoline resistance.
2. Discussion of the Prior Art
The recent social demand for preserving a good environment has resulted in enforcement of regulations for control of motor vehicle exhausts, and new and improved engine designs have been developed to meet these regulations. To cope with the new development in engines, many important maintenance parts of automobiles are made of synthetic rubbers having all of heat resistance, gasoline (oil) resistance, low temperature resistance and weatherability.
Among existing synthetic rubbers, an acrylonitrile-butadiene copolymer rubber (to be referred to as NBR hereinbelow) has found by far the widest application as hoses, gaskets, O-rings and oil seals because of its well-balanced combination of various properties. However, because of its unsatisfactory weatherability, NBR is frequently used protected with a cover material such as chloroprene rubber or chlorosulfonated polyethylene in such an application as hoses, and is rarely used alone.
As a result of the new and improved engine designs, the ambient atmosphere of the engine tends to attain a higher temperature than in conventional designs, and this causes heat deterioration of gasoline to form degraded gasoline known in the art as "sour gasoline."
NBR has superior gasoline resistance, but on contact with sour gasoline, will undergo degradation involving hardening. Hence, automobile parts made of NBR involve a danger of performance failure within a relatively short period of service.
Blending with a vinyl chloride resin, an ethylene/propylene copolymer rubber, etc. is one possible way of improving the weatherability of NBR. Certainly, this method brings about an improvement in weatherability, but is not practical because the blending of the vinyl chloride resin causes poor low temperature resistance and the mixing of the ethylene/propylene copolymer results in poor oil resistance.